Roll-pin support for turbomachine blades



United States Patent ROLL-PIN SUPPORT FOR TURBOMACHINE BLADES Henry Shapiro, Los Angeles, Thomas B. Martin, Pacific Palisades, and Berry W. Foster, Orange Cove, Calif., assignors to General Electric Company, a corporation of New York Application October 12, 1955, Serial No. 540,127

2 Claims. (Cl. 25377) The present invention relates to a roll-pin turbomachine blade support and, more particularly, to a low stress roll-pin support for light-weight blades which allows the blade to lean freely into the centrifugal field for its stiffness. I

Numerous blade constructions and configurations of turbomachine blades and blade supports have been suggested to effect reductions in rotor weight and permit lighter overall design. Of these, the flexible blade which leans freely into the centrifugal field and thereby obtains its stiffness has proved especially interesting. However, the advantages of the flexible blade have not been fully realized heretofore due to the lack of a completely reliable blade support. The hinged pin support previously used has a relatively high coeflicient of friction at the sliding surface and tends to seize or lock under the high temperatures and pressures of turbomachine operation;

The roll-pin support of the present invention overcomes the disadvantages ofprior supports and permits full utilization of flexible blades by providing a low stress pin connection between the blade and the wheel wherein the mounting pin is received within a sleeve secured to the wheel. The low stress rolling action between the mounting pin and the sleeve permits substantial reductions in the blade root bending stress and the vibratory bending stress and eliminates any tendency to seize or lock in one position.

An object of the present invention is the provision of a roll-pin support for light-weight turbomachine blades which substantially reduces the vibratory and the blade root bending stresses therein.

An additional object is to provide low-stress rolling action between the contacting surfaces of the blade and wheel.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawing wherein:

Fig. 1 is a perspective view of a rotor embodying the blade support of the present invention.

Fig. 2 is a sectional view taken along lines 2-2 of Fig. 1.

Fig. 3 is a perspective view of a blade partly broken away showing the line contact between the pin and the sleeve.

Fig. 4 is a plan view of a portion of a rotor partly broken away to show the sleeve inserted within the wheel.

Referring more particularly to Fig. l of the drawing, the rotor construction 11 includes the wheel 12 and one or more blades 13. The gas path sections 14 and 15 are formed integrally around its peripheral edge and are spaced at intervals with the blades received between adjacent sections. Inwardly of each of the spaces between adjacent gas path sections, the wheel 12 is pierced by transverse openings 16 and 17. The narrow portions of the wheel above each of the transverse openings 16 ice and 17 are sawed or otherwise cut through as at 18 to d prevent the concentration of stresses within this area.

The blade 13 is provided with a platform section 19 which, when the blade is in position on the wheel, bridges the space between adjacent gas path sections 14 and 15 and prevents leakage of gas therebetween.

As can be seen in Fig. 2, a pair of tangs or cars 21 and 22 depend from the lower surface of the platform 19 near the opposite axial extremities thereof. A cylindrical sleeve or bushing 23 is inserted through the opening 17 in the wheel and extends between the inner edges of the tangs21 and 22. A pair of aligned openings 24 and 25 are provided in the tangs 21 and 22 and are open to theinterior of the sleeve 23. A pin 26 is passed through the sleeve 23 with its opposite ends received within the openings 24 and 25. The sleeve 23 is retained within the opening 17 and the pin 26 within the openings 24 and 25 by any suitable means, such as, press fitting, etc.

The mounting pin 26, as shown in Fig. 3, is of smaller blade and thence through the tangs to the pin, thereby distributing the load over the entire bearing length so the pin maintains contact with the bushing throughout its length rather than contact and thus concentrating the loads at the ends only.

Referring to Fig. 4, when the blade is properly mounted on the wheel the platform is spaced slightly from the adjacent gas path sections to allow pivotal movement of the blade through a small are. This spacing is suflicient to permit freedom of movement of the blade, but is not large enough to create any serious leakage problems.

The successful use of a flexible blade depends upon the blade being free to move with respect to the wheel on which it is mounted. This is insured in the present invention by the line contact between the mounting pin and the inner surface of the sleeve or bushing and the rolling action which occurs between these contacting surfaces. When the rotor wheel is turning, the centrifugal force acting on the blades urges the pin into contact with the sleeve. Under the influence of the gas load the blade moves relative to the wheel. When the blade moves relative to the wheel the line of contact between the pin and the inner surface of the sleeve moves to one side of a radial line extending between the diametrical center of the wheel and the center of the sleeve in which it is positioned. This creates a moment arm for the centrifugal forces of the blade, generating a centrifugal moment which opposes the gas load pressures. As the blade continues to move, the moment arm is lengthened and the centrifugal moment is increased until it balances the gas load pressures and the blade is in equilibrium. Since the forces acting on the blades are in equilibrium, the blade root bending stresses are substantially reduced. In addition, as the blade moves to new positions of equilibrium under the varying pressures of the gas load, some frictional rubbing is introduced between the pin and the inner surface of the sleeve and between the ends of the sleeve and the inner surfaces of the tangs. This frictional rubbing introduces much needed damping into the vibrating blade. The amount of total damping introduced by the roll-pin blade support of the present invention is up to six times as much as Patented Mar. 15,1960

that introduced by presently used blade supports. The importance of this damping is evident when it is realized that vibratory amplitude varies inversely with the amount of damping at resonance.

Obviously, many modifications and variations of the teachings. It is therefore, to'be understood that within the scope of the appended claims, theinvention' may be practiced otherwise than as specifically described.

tending beyond the opposite faces thereof; a' pair .of

spaced, tangs depending from the lower surface of the blade platform, said tangs overlying the ends or the bushing; and 'a mounting pin passed through the bushing j and secured at its opposite ends to said, tan'gs, the diameter of said pin being substantially smaller than. the

internal diameter of the bushing, and said pin having an arcuate portion making line contact with the inner surface of said bushing; said pin and bushingibeing' dimensioned to flex together under the application of centrifugal and aerodynamic loads whereby rolling action occurs along a line contact between the pin and the inner surface of the bushing overothe entire length of the bushing when the blade is moved relative to the" wheel.

2; In a turbomachine rotor including a wheel and a blade having a platform thereou: anelongated cylin-' eczema present invention are possible in :the light .of the above dric al bushing positioned in the wheel and of greater length than the-wheel thickness and having its e'nds 'ex'e tending beyond the opposite faces thereof; a pair of spaced Vtangs depending from the lower surface of the passed through the bushing and secured at its opposite ends to saidtangs; the diameter of said pin being substantially smaller than the internal diameter of the bushin; and said pin making line contact with the inner: surface of the bushing;v said pin and bushing: being dimentioned to flex'together under the application of centrifugal and aerodynamic loads whereby rolling action occurs along aline contact between the pin and the inner surface of the bushing over the entire length of the bushing when the blade) is moved relative to the wheel.

References Cited in the file of this patent UNITED STATES rrrrrarrrs 1,802,648 Heath1 v Apr. 28,, 1931 2326 Kmofi. v Aug, to, 1943i- 2,436,( )87 Benson Feb. 17, 1948' 2,537,739 vChilton. v.. Jane 9, 1 ,951 2,819,869 Meyer Jan. 14', 1958 I Y I FOREIGN PATENTS 621,315 Great. Britain Apr. 7, 1949' 667,979 Great Britain Mar. 12', 1952 9189,0 13 France May 1'6, 1951" t 989,556 France .....7. May 23, 1951 1,097,487

France Feb. 16, 1955 

